Strain gage transducer



Nov. 17, 1959 SHlH-YING LEE ETAL 2,913,692

STRAIN GAGE TRANSDUCER Filed Dec. 17, 1956 INVENTORS SHlH-YING LEE YAO TZU LI KENWAY, JENNEY, WlTTER & HILDRETH ATTORNEYS eit d ar M STRAIN GAGE TRANSDUCER Sllih-Ying Lee and Yao Tzu Li, Watertown, Mass. Application December 17, 1956, Serial No. 628,710

2 Claims. (Cl. 338-6) The present invention relates to strain gage transducers and more particularly to strain gages of the unbonded yp One object of the present invention is to provide a strain gage transducer of simple and efficient construction, and another object is to provide a transducer in which a relatively large motion is accommodated with only small resistance to movement.

With these objects in view the present invention comprises a central supporting member or spider, together with two armatures mounted for relative movement there with, in combination with strain wires wound between the central support and the movable armatures, which wires may be at an angle of nearly 90 with respect to the direction of movement of the armature. The apparatus is particularly useful as a pick-up for low pressures where a considerable mechanical motion of the diaphragm is attained through the use of a so diaphragm, and the resistance to motion is necessarily small.

In the accompanying drawings Fig. l is a plan view of the preferred form of transducer on a greatly enlarged scale;

Fig. 2 is an end elevation;

Fig. 3 is a side elevation; and

Fig. 4 is a diagram illustrating the electrical connections.

The preferred form of the invention comprises a central supporting member or spider 6 in the general shape of a cross having four radiating arms 8, 10, '12 and 14. The arms 8 and 12 are opposed to each other, and the arms and 14 are opposed to each other. Upstanding from the upper surface of the arm 10 is a leg 16 to which is attached a crossbar 18. A similar leg 20' depends from the bottom surface of the arm 14 and a crossbar 24 is attached thereto. The entire cross, the legs and the crossbars are preferably formed as a single piece, as by an investment casting.

Four terminal wires 24, 26, 28 and 30 are mounted at the ends of the respective arms, being received in glass or plastic insulating bushings, one of which is indicated at 32 for the terminal 30. The wires are originally straight but are bent at their ends in the manner indicated in the drawings to serve as terminals for the strain wires.

A spindle 34 passes through a central opening at the intersection of the arms of the cross. A movable member or armature is secured to the spindle 34 on each side of the central supporting member. The upper armature is indicated at 35 and the lower armature at 36. Each armature is provided with a ledge 38. A flexible supporting plate 40'of sheet metal in a generally triangular shape is attached to the crossbar 18 and to the ledge 38 of the upper armature 35, and a similar triangular plate 42 is connected between the crossbar 22 and the ledge 38 of the lower armature 36. The plates 40 and 42 are flexible and permit axial motion of the armatures, but restrain the armatures from any rotational or lateral motion with respect to the cross-shaped central support.

Central supporting rods 44 and 46 pass sidewise through arms 10 and 14 of the central supporting member. They are of insulating material, such as sapphire. A supporting rod 48 of similar type is passed through the armature 35 and another similar rod 50 is passed through the armature 36. A strain wire winding 52 is wound on the rods 44 and 48 on one side of the arms 10 and 14, and a second strain winding 54 is similarly wound on the same rods at the other side of the arms. In a similar fashion two windings 56 and 58 are wound on the rods 46 and 50. As shown particularly in the diagram of Fig. 4, the winding 52 is connected to terminals 26 and 28, winding 54 is connected between terminals 24 and 30, and winding 56 is connected between terminals 28 and 30, and winding 58 is connected between terminals 24 and 26. The windings are wound under some initial tension, as is well known to those skilled in the art of unbonded strain gages.

Under normal conditions the plates 40 and 42 maintain the armatures 3'5 and 36 in a neutral position so that all of the strain wires are equally stressed. However, upon a longitudinal motion of the spindle the wires are unequally stressed. For example, if the spindle 34 is moved upwardly as viewed in Fig. 2, the wires 52 and 54 are stretched while the tension on the windings 56 and 58 is relaxed. In the bridge of Fig. 4, the wires under increased tension form two opposite arms of the bridge and the wires under decreased tension form the other two arms of the bridge. A substantial signal may thus be obtained. If the spindle 34 is moved downwardly, a similar but opposite signal will be obtained.

It will be observed that wires 52 and 56 on one side of the unit may be considered to constitute one measuring pair, while wires 54 and 58, on the other side of the unit, constitute a second pair. A single pair suifices for signal generation, but a larger signal is obtained by the use of two pairs.

The apparatus provides adequate temperature compensation, since expansion or contraction due to a change in temperature causes equal strain in the several arms.

It will be observed that the axis of the spindle 34 is at an angle of nearly from the longitudinal axes of the various windings. A considerable motion of the spindle is thus required to strain the windings. The strain in each stretch of any wire is proportional to the cosine of the above-mentioned angle. The apparatus is therefore most useful in a service where a fairly considerable motion is attained, as in the case of a low pressure pickup in which a soft diaphragm may be used. The arrangement of wires provides an exceptionally compact arrangement in longitudinal dimension.

Having thus described my invention, I claim:

1. A strain gage transducer comprising a central support member having an opening, a spindle passing freely through the opening, an upper armature attached to the spindle above the support member and extending laterally therefrom and having a ledge on its upper surface at the end of the armature remote from the spindle, a lower armature attached to the spindle below the support member and extending laterally therefrom in the direction opposite to the upper armature, and having a ledge on its lower surface at the end of the armature remote from the spindle, the upper part of the support member having a supporting surface level with the ledge of the upper armature and at the opposite side of the spindle from said ledge, the lower part of the support member having a supporting surface level with the ledge of the lower armature and at the opposite side of the spindle from said ledge, flexible plates attached to said supporting surfaces and their corresponding ledges to support the armatures while permitting movement of the spindle and armatures lohgitudinally of the spindle, and a strain gage wire References Cited in the file of this patent I mounted between the central support and each aIma- UNITED STATES PATENTS ture.

2. A strain gage-transducer according to claim 1 in 21,721,919 L1 et 1955 which each strain gage wire is mounted on its armature 5 2,783,342 Statham 261 1957 at 'a point remote from the spindle and extends slantwise with respect to the spindle to a mounting on the support member. 

